Immunization against bacterial or viral infection has greatly contributed to relief from infectious disease. Generally, immunization relies on administering an inactivated or attenuated pathogen to the subject to be immunized. For example, hepatitis B vaccines can be made by inactivating viral particles with formaldehyde, while some polio vaccines consist of attenuated polio strains that cannot mount a full-scale infection. In either case, the subject's immune system is stimulated to mount a protective immune response by interacting with the inactivated or attenuated pathogen. See, e.g., Kuby, 1997, Immunology W.H. Freeman and Company, New York.
This approach has proved successful for immunizing against a number of pathogens. Indeed, many afflictions that plagued mankind for recorded history have been essentially eliminated by immunization with attenuated or inactivated pathogens. See id. Nonetheless, this approach is not effective to immunize against infection by many pathogens that continue to pose significant public health problems. In particular, no vaccine presently exists that has been approved for immunization against Pseudomonas ssp. infection. The absence of such a vaccine presents significant public health problems.
For example, Pseudomonas aeruginosa infections account for between 10% and 20% of all infections acquired in most hospitals. Pseudomonas commonly infects patients with a variety of other afflictions, such as cystic fibrosis, burns, organ transplants, and intravenous-drug addiction. Such infections can lead to serious conditions, including endophthalmitis, endocarditis, meningitis, pneumonia, and septicemia. In subjects with cystic fibrosis, Pseudomonas aeruginosa colonization of the lungs represents a significant negative milestone in the progression of this disease. See, for example, Ratgen, 2001, Int J Antimicrob Agents 17:93-96. Once colonized, such subjects suffer both the damaging effects of virulence factors secreted by the bacteria and the inflammatory response of the host immune system.
Initially, Pseudomonas colonization of the lungs requires adhesion of the bacteria to the lung epithelium. Such adhesion is mediated, in part, by an interaction between the Pseudomonas pilus and extracellular glycoproteins present on lung epithelial cells. The Pseudomonas pilus is composed of many subunits of Type IV pilin protein that polymerize to form the pilus. See, e.g., Forest et al., 1997, Gene 192(1): 165-9 and Parge, 1995, Nature 378(6552):32-8.
More specifically, Pseudomonas aeruginosa Type IV pilin proteins bind to asialoGM1 receptors on epithelial cells. See, e.g., Saiman et al., 1993, J. Clin. Invest. 92 (4): 1875-80; Sheth et al., 1994, Mol. Microbiol. 11(4):715-23; Imundo et al., 1995, Proc. Natl. Acad. Sci. USA 92(7):3019-23; and Hahn, 1997, Gene 192(1):99-108. The portion of pilin responsible for this interaction has been mapped to a C-terminal loop present in the tip of the bacterial pilus. See Lee et al., 1994, Mol. Microbiol. 11(4):705-13. This C-terminal loop is formed by amino acids 122-148 of the pilin protein in a β-turn loop subtended from a disulfide bond. See, e.g., Campbell et al., 1997, Biochemistry 36(42):12791-80; Campbell et al., 1997, J. Mol. Biol. 267(2):382-402; Hazes et al., 2000, J. Mol. Biol. 299(4):1005-1017; and McInnes et al., 1993, Biochemistry 32(49):13432-40. Disruption of the interaction between this region of Type IV pilin and asialoGM1 receptors prevents adherence of the bacteria to the epithelial cell and prevents effective bacterial colonization. See Hertle et al., 2001, Infect. Immun. 69:6962-6969.
Previous efforts to vaccinate against Pseudomonas infection by immunizing with Pseudomonas pilin protein or derivatives thereof have yielded lackluster results. Immunization with whole pilin protein, with or without adjuvant, is not effective to prevent Pseudomonas infection because the most immunogenic portion of the pilin protein is not the loop that mediates adherence to epithelial cells. See, e.g., Sastry et al., 1985, Ca. J. Biochem. Cell Biol. 63:284-291. Thus, antibodies raised against the entire pilin protein are principally specific for another region of the pilin protein and thus do not disrupt the interaction that mediates bacterial adherence.
Vaccine compositions that comprise only the C-terminal loop (residues 128-144) of the pilin protein have also been tested for the ability to protect against Pseudomonas infection. See, e.g., U.S. Pat. Nos. 5,612,036 and 5,445,818. These vaccines induce a humoral immune response specific for the C-terminal loop, and antibodies produced in the response can prevent Pseudomonas adherence to epithelial cells in vitro. Experiments by these researchers showed that pilin vaccine compositions that comprise the same adjuvant and peptides that correspond to amino acids 121-148 of Type IV pilin were not effective to induce a protective immune response.
Further, chimeric proteins constructed from Pseudomonas exotoxin A (“PE”) derivatives and peptides corresponding to amino acids 128-144 of Type IV pilin protein have also been tested for their ability to induce a protective immune response. See Hertle et al., 2001, Infect. Immun. 69:6962-6969. Nonetheless, none of these attempts has to date resulted in a vaccine that has been approved as effective to immunize against Pseudomonas infection. Thus, there remains an unmet need for methods and compositions for immunizing against Pseudomonas infection.